1. Field of the Invention
This invention relates to an intrusion detection system which detects a human body as an infrared ray radiating object by means of pyroelectric infrared sensor incorporating a plurality of pyroelectric detectors, and identifies the intrusion of a visitor or an intruder.
2. Description of the Prior Art
Conventionally, there are a variety of intrusion detection systems which are widely made available by conventional stores and individual homes for detecting and alarming of visitation or intrusion of any person. Normally, most of these conventional intrusion detection systems use pyroelectric infrared sensors incorporating pyroelectric detectors for detecting an approaching or moving human body as the infrared ray radiating object.
Any conventional pyroelectric infrared sensor outputs a detection signal in response to varied infrared ray energy incident upon itself. For example, recently, there are a wide variety of alarms against intrusion or systems for advising store employees of visiting buyers which detect visitation or intrusion of any person via the pyroelectric infrared sensor using infrared rays radiated from the human body. However, since any of those conventional pyroelectric infrared sensors output a detected signal only at the moment when the quantity of incident infrared energy varies, it merely detects the human body intruding himself into the surveillance region or leaving it, and thus, it cannot correctly identify the direction of the movement of the detected human body. In other words, it cannot correctly identify whether he is still on the way of intrusion or leaving the surveillance region.
Nevertheless, in order to gain information in conjunction with the direction of the movement of the human body, any conventional pyroelectric infrared sensor can also identify the direction of the movement of human body by identifying which one of the two pyroelectric infrared sensors first outputs detect-signals. Nevertheless, this conventional system needs the provision of two optical units, and yet, this also needs installation of more expanded and complex facilities, thus eventually resulting in increased cost.
To eliminate those problems mentioned above, Japanese Utility Model Publication No. 61-30180 (1986) proposes a constitution of pyroelectric infrared sensors, the detail of which is shown in FIGS. 1 and 2.
A pair of pyroelectric detectors 91 and 92 are installed in the vertical direction, while each of these pyroelectric detectors is provided with electrodes 91b and 92b without overlapping each other. The remaining portions 91a and 92a outside of electrodes 91b and 92b respectively allow permeation of infrared rays. This allows each of these electrodes 91b and 92b to independently output a specific amount of voltage and thus detect the direction of the movement of a human body by comparing voltages output from those pyroelectric detectors. On the other hand, the above constitution causes each of these pyroelectric detectors 91 and 92 to sensitively react to atmospheric temperature, and as a result, these pyroelectric detectors 91 and 92 often generate incorrect detection signals other than normal ones.
Conventionally, in order to prevent any of those incorrect signals from being generated, a pair of pyroelectric detectors are connected to each other in parallel or in series to constitute dual-elements so that the polarity of these elements can be opposite from each other, thus effectively offsetting any of those incorrectly generated detection signals caused by variable atmospheric temperature. Consequently, the dual-element constitution of the pyroelectric detector proposed by the above-cited prior art can prevent incorrect detection signals from being generated. On the other hand, since this constitution needs to employ 4 pyroelectric detectors which are aligned with each other at a certain interval in a casing, it in turn obliges manufacturers to design greater-size sensors and a more complex constitution of the sensor, thus eventually incurring costwise disadvantage.
On the other hand, some of conventional incoming visitor announcing systems introduced to stores identify the direction of the movement of people passing by path and generate audio messages such as "welcome your visit to us" for those who are entering into stores and "thank you for your shopping made with us" for those who are leaving stores for example. However, it is quite important for those stores to have the incoming visitor announcing system securely identify incoming visitors and advise store employees of actual visitors entering the stores.